JPH10316701A - Cellulose acetate and dope containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cellulose acetate which is excellent in optical properties and can give a film having high releasability from the support when cast. SOLUTION: A film is produced by a casting process from a dope containing a cellulose acetate in which the carboxyl groups bonded to a cellulose acetate and/or a hemicellulose acetate are in an acid form, a cellulose acetate containing an acid having an acid dissociation index pKa of 1.95-4.50 (e.g. citric acid) or a salt thereof (e.g. an alkali metal or alkaline earth metal salt) or a cellulose acetate having a total alkali metal and alkaline earth metal content ranging from the effective amount to 5.5×10<-6> equivalent (in terms of ionic equivalent). The cellulose acetate is useful for also spinning. The cellulose acetates include diacetates and triacetates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cellulose acetate useful for forming films (protective films for polarizing plates, color filters, films for photographic light-sensitive materials, etc.) and fibers, and dopes containing the same.

[0002]

2. Description of the Related Art Cellulose triacetate film is
It is strong and has high dimensional stability, heat resistance, optical isotropy, etc.
It is used for applications such as a support for an optical film (for example, a support film for a photographic light-sensitive material), a polarizing plate protective film (a liquid crystal protective film) in a liquid crystal display device, and a color filter. Therefore, the cellulose triacetate film is required to have low optical properties, for example, a low yellowness index, a low haze and a low birefringence, and high transparency. In the case where fibers are produced using a solution (dope) containing a cellulose acetate such as cellulose diacetate and a solvent, high spinnability is required.

[0003] In order to enhance the optical characteristics of the cellulose acetate film, usually, a cotton linter pulp, a softwood pulp or a hardwood pulp is acetylated, and a solution (dope) containing the produced cellulose acetate and a solvent is flowed on a support. It is manufactured by a casting method in which a film is spread and a film is peeled from a support. However, the use of linter pulp increases the cost of cellulose acetate. Further, among softwood pulp, high-purity pulp has a problem in stable supply of raw materials, and low-purity pulp tends to have low transparency of cellulose acetate. On the other hand, when hardwood pulp is used, although it is advantageous in terms of cost, the releasability from the support decreases, and it is difficult to improve the surface smoothness and productivity of the film. Further, in the case of cellulose acetate using low-purity wood pulp, the stability of the dope and the filterability are impaired, and the spinnability is reduced.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cellulose acetate having high releasability from a support in a casting method and a dope containing the same. It is another object of the present invention to provide a cellulose acetate having high optical properties as well as high releasability from a support in a casting method and a dope containing the same. Still another object of the present invention is to provide a cellulose acetate having a high spinnability when producing a fiber using a cellulose acetate dope, and a dope containing the same. Still another object of the present invention is to provide a cellulose acetate which has releasability, optical properties and spinnability and is excellent in heat resistance.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to achieve the above object, and found that the form of carboxyl groups bonded to cellulose acetate and / or hemicellulose acetate, alkali metal or alkali in cellulose acetate, and the like. The present inventors have found that the content of the earth metal greatly affects the peelability, transparency and spinnability of the dope of the film, and completed the present invention.

That is, the cellulose acetate of the present invention includes (1) cellulose acetate in which at least a part of carboxyl groups bonded to cellulose acetate and / or hemicellulose acetate is present in an acid form;
(2) The acid dissociation index pKa in an aqueous solution is from 1.93 to 4.
Cellulose acetate containing at least one selected from the group consisting of at least one acid selected from the group consisting of an alkali metal salt of the acid and an alkaline earth metal salt of the acid; and (3) alkali metal and alkaline earth metal in 1 g of cellulose acetate. And cellulose acetate having a total content of not less than an effective amount and not more than 5.5 × 10 ⁻⁶ equivalent (in terms of ion equivalent). Furthermore, the cellulose acetate of the present invention also includes a cellulose acetate obtained by combining the above embodiments (1) to (3). Furthermore, in the present invention, the pH of the slurry is adjusted to 4.
By adjusting the content to 5 to 6.0, cellulose acetate having heat resistance is also included.

[0007] The dope of the present invention contains at least one kind of cellulose acetate among the above-mentioned cellulose acetates. Further, the dope of the present invention comprises (a) cellulose acetate and (b) an acid dissociation index pKa in an aqueous solution.
Of at least 1.93 to 4.50, and a dope containing at least one selected from an alkali metal salt of the acid and an alkaline earth metal salt of the acid. Furthermore, the present invention also includes a method for improving the releasability of a film from a support or the spinnability during fiber production by using the dope.

[0008] In the case of a multi-stage dissociating acid, the value of the acid dissociation index pKa may differ depending on the number of dissociation stages. In the present specification, the “acid dissociation index pKa 1.93 to 4.50” means that the acid dissociation index in at least the first stage (dissociation stage 1) is in the range of pKa 1.93 to 4.50. .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The cellulose acetate of the present invention can be obtained by acetylating pulp. The type of the pulp is not particularly limited, and various types of pulp can be used. Typically, at least one type selected from wood pulp (hardwood pulp, softwood pulp) and linter pulp can be used. You may use together with pulp. The α-cellulose content which is an index of pulp purity is, for example, 90 to 100% by weight.
In wood pulp, typically 92
About 98%. In the present invention, low-purity pulp, for example, α-cellulose content of 90 to 97% (especially 92 to 9)
6%) pulp can also be used. Of these pulp, wood pulp is usually used. As described above, cellulose acetate made from hardwood pulp is generally inferior in peelability of a film by a casting method, and cellulose acetate made from softwood pulp is generally
Poor optical properties such as transparency and spinnability. The present invention can improve the optical properties such as the releasability of the cellulose acetate film and the transparency of the cellulose acetate and the spinnability even with such a wood pulp.

[0010] Cellulose acetate can be produced by a conventional method such as a sulfuric acid catalyst method, an acetic acid method and a methylene chloride method. Cellulose acetate is usually
After pulp (cellulose) is activated with acetic acid (activation step), triacetate is prepared with acetic anhydride using a sulfuric acid catalyst (acetylation step), and the degree of acetylation is reduced by saponification (hydrolysis) and aging. It can be manufactured by adjusting (saponification / aging process). In this method, the activation step can be performed by treating pulp (cellulose), for example, by spraying acetic acid or aqueous acetic acid, or immersing in acetic acid or aqueous acetic acid. 10 to 100 parts by weight, preferably 20 to 80 parts by weight, more preferably 3 to 100 parts by weight, based on 100 parts by weight of pulp (cellulose).
It is about 0 to 60 parts by weight. The amount of acetic anhydride used in the acetylation step (acetylation step) can be selected within the range of the above-mentioned acetylation degree. For example, 230 to 300 parts by weight, preferably 240 parts by weight, per 100 parts by weight of pulp (cellulose).
To 290 parts by weight, more preferably about 250 to 280 parts by weight. In the acetylation step, acetic acid is usually used as a solvent. The amount of acetic acid used is, for example, about 200 to 700 parts by weight, preferably about 300 to 600 parts by weight, and more preferably about 350 to 500 parts by weight, based on 100 parts by weight of pulp (cellulose). As the acetylation or aging catalyst, sulfuric acid is usually used. The amount of sulfuric acid used is usually from 1 to 1 based on 100 parts by weight of cellulose.
The amount is 5 parts by weight, preferably 5 to 15 parts by weight, particularly about 5 to 10 parts by weight. Saponification and aging can be performed, for example, at a temperature of about 50 to 70 ° C.

In order to improve the optical properties of cellulose acetate, the produced cellulose acetate may be treated with an oxidizing agent after an appropriate step in the production process of cellulose acetate, for example, after completion of acetylation, saponification and ripening. . Examples of the oxidizing agent include hydrogen peroxide; peracids such as formic acid, peracetic acid, and perbenzoic acid; and organic peroxides such as diacetyl peroxide. The oxidizing agents can be used alone or in combination of two or more. Preferred oxidizing agents include those which can be easily removed from cellulose acetate and have low residual properties,
For example, hydrogen peroxide, formic acid, and peracetic acid are included, and hydrogen peroxide and peracetic acid are particularly preferable. The amount of the oxidizing agent can be selected according to the level of the desired optical property. For example, the amount is 0.01 to 100 parts by weight of cellulose acetate.
5 parts by weight, preferably 0.1 to 2.5 parts by weight, in particular 0.
It is about 1 to 1 part by weight. The treatment with the oxidizing agent can be performed, for example, at about 20 to 100 ° C., preferably about 30 to 70 ° C., depending on the type of the oxidizing agent.

The average degree of acetylation of cellulose acetate can be selected from the range of about 30 to 62.5% depending on the use and characteristics. However, industrially useful cellulose acetate is usually cellulose diacetate to cellulose triacetate. is there. The average degree of acetylation of cellulose acetate is, for example, 43.7 to 62.5% (average degree of substitution of acetyl group 1.7 to 3.0), preferably 45 to 62.5%.
62.5% (average degree of substitution 1.8 to 3.0), more preferably 48 to 62.5% (average degree of substitution 2.0 to 3.0)
It is about. Cellulose triacetate usually has an average degree of acetylation of 58 to 62.5%, preferably 58.5 to 62, in order to enhance dimensional stability, moisture resistance, heat resistance and the like.
%, More preferably 59 to 62% (for example, 60 to 6%).
1%).

The degree of acetylation means the amount of bound acetic acid, and means the weight percentage of bound acetic acid per unit weight of cellulose.
It can be measured according to the method for measuring the degree of acetylation of TM: D-817-91 (test method for cellulose acetate or the like). Specifically, dried cellulose acetate 1.9
g was precisely weighed and dissolved in 150 ml of a mixed solvent of acetone and dimethylsulfoxide (volume ratio: 4: 1).
Add 30 ml of aqueous sodium hydroxide solution, and add
Time saponification. Phenolphthalein is added as an indicator and excess sodium hydroxide is titrated with 1N sulfuric acid (concentration factor: F). A blank test is performed in the same manner as described above, and the acetylation degree is calculated according to the following equation. Degree of acetylation (%) = [6.5 × (BA) × F] / W (where A is the titer (ml) of 1N-sulfuric acid in the sample, B
Is the titer (ml) of 1N-sulfuric acid in the blank test, F is the concentration factor of 1N-sulfuric acid, and W is the weight of the sample).

Further, the degree of polymerization of cellulose acetate is 200 to 400, preferably 250.
To 400, more preferably 270 to 400 (for example,
290-400), and usually has a viscosity average polymerization degree of 2
It is about 70 to 350. The average degree of polymerization can be measured by the intrinsic viscosity method of Uda et al. (Uda Kazuo, Saito Hideo, Journal of the Textile Society of Japan, Vol. 18, No. 1, pp. 105-120, 1962). At that time, the solvent can be selected according to the degree of acetylation of the cellulose acetate. For example, in the case of cellulose triacetate, cellulose triacetate is dissolved in a mixed solution of methylene chloride / methanol = 9/1 (weight ratio),
A solution having a predetermined concentration c (2.00 g / L) is prepared. This solution is poured into an Ostwald viscometer, and the time (second) t during which the solution passes between the marking lines of the viscometer at 25 ° C. is measured. On the other hand, for the mixed solvent alone, the passage time (second) t0 is measured in the same manner as described above, and the viscosity average polymerization degree can be calculated according to the following equation. η _rel = t / t0 [η] = (lnη _rel ) / c DP = [η] / (6 × 10 ^-4 ) (where t is the solution transit time (seconds), and t0 is the solvent transit time ( Sec), c is the concentration of cellulose triacetate in the solution (g / L), η _rel is the relative viscosity, [η] is the intrinsic viscosity, D
P indicates an average degree of polymerization. When a mixed solvent of methylene chloride / methanol = 9/1 (weight ratio) is used, the 6% by weight solution viscosity of cellulose triacetate is, for example, 200 to 700 cp.
s, preferably 250-600 cps, especially 250-5
It is about 00 cps.

Such a cellulose acetate is usually used in order to improve the stability. In order to improve the stability, a heat-resistant stabilizer such as an alkali metal (lithium, potassium, sodium or the like) or a salt or a compound thereof, or an alkaline earth metal (calcium or magnesium) is used. , Strontium, barium, etc.) or a salt or compound thereof.

The cellulose acetate of the present invention mainly comprises
It can be roughly divided into the following three embodiments (1) to (3). (1) Cellulose acetate in which at least a part of carboxyl groups bonded to cellulose acetate and / or hemicellulose acetate is in an acid form. (2) The acid dissociation index pKa in an aqueous solution is from 1.93 to 4.
Cellulose acetate containing at least one selected from the group consisting of at least one of 50, an alkali metal salt of the acid and an alkaline earth metal salt of the acid. (3) Cellulose acetate having a total content of alkali metal and alkaline earth metal in 1 g of cellulose acetate of not less than an effective amount and not more than 5.5 × 10 ⁻⁶ equivalent (in terms of ion equivalent).

Further, the cellulose acetate of the present invention also includes the following cellulose acetates (4) to (7) in which the above embodiments (1) to (3) are combined. (4) A combination of the above (1) and (2), that is, at least one acid having an acid dissociation index pKa in an aqueous solution of 1.93 to 4.50, an alkali metal salt of this acid, and the acid Cellulose acetate containing at least one selected from alkaline earth metal salts, wherein at least a part of a carboxyl group bonded to cellulose acetate and / or hemicellulose acetate exists in an acid form. (5) The combination of (1) and (3), that is, the total content of alkali metal and alkaline earth metal in 1 g of cellulose acetate is not less than the effective amount and is 5.5 ×
Cellulose acetate having not more than 10 ^-6 equivalents (in terms of ion equivalents), wherein at least a part of carboxyl groups integrated into cellulose acetate and / or hemicellulose acetate is present in an acid form.

(6) a combination of the above (2) and (3),
That is, the acid dissociation index pKa in the aqueous solution is 1.93 to
At least one acid selected from the group consisting of at least one acid selected from the group consisting of an alkali metal salt of the acid and an alkaline earth metal salt of the acid;
g of cellulose acetate whose total equivalent weight of alkali metal and alkaline earth metal is not less than an effective amount and not more than 5.5 × 10 ⁻⁶ equivalents (in terms of ion equivalents). (7) The above (1) and (2) ) And (3), that is, the acid dissociation index pKa in an aqueous solution is 1.93 to 4.5.
0, at least one selected from the group consisting of an alkali metal salt of the acid and an alkaline earth metal salt of the acid, and a total content of the alkali metal and the alkaline earth metal in 1 g of cellulose acetate. A cellulose acetate which is not less than an effective amount and not more than 5.5 × 10 ⁻⁶ equivalents (in terms of ion equivalents), and at least a part of carboxyl groups integrated into cellulose acetate and / or hemicellulose acetate is present in an acid form.

[Cellulose Acetate of Embodiments (1), (4), (5) and (7)] The cellulose acetate of the embodiments (1), (4), (5) and (7) binds to cellulose acetate and / or hemicellulose acetate. At least a part of the carboxyl group is a free acid-type carboxyl group, and not all of the carboxyl groups are metal salt-type carboxyl groups (for example, the alkali metal salt and alkaline earth metal salt-type carboxyl group). In a preferred cellulose acetate, at least 30 mol%, preferably 5
0 to 100 mol%, particularly about 70 to 100 mol%, is composed of free carboxyl groups.

[Cellulose Acetate of Embodiments (2), (4), (6) and (7)] In the cellulose acetate of Embodiments (2), (4), (6) and (7), the acid dissociation index pKa is 1.93 to 4.50. [Preferably 2.0 to 4.4, more preferably 2.2 to 4.3.
(For example, about 2.5 to 4.0, especially about 2.6 to 4.3 (for example, about 2.6 to 4.0)] include inorganic acids and organic acids. For the pKa of acids, see "Revision 3
Chemical Handbook, Basic Edition II "(edited by The Chemical Society of Japan, published by Maruzen Co., Ltd.). Hereinafter, the acid dissociation index pKa is shown in parentheses together with specific examples of the acid.

As the inorganic acid, for example, HClO ₂
(2.31), HOCN (3.48), molybdic acid (H ₂ Mo)
O ₄ , 3.62), HNO ₂ (3.15), phosphoric acid (H ₃ P
O ₄ , 2.15), tripolyphosphoric acid (H ₅ P ₃ O ₁₀ , 2.
0), vanadic acid (H ₃ VO ₄ , 3.78) and the like.

Examples of the organic acid include aliphatic monocarboxylic acids [formic acid (3.55), oxaloacetic acid (2.27), cyanoacetic acid (2.47), phenylacetic acid (4.10), phenoxyacetic acid (2.99), and fluoroacetic acid (2.59). , Chloroacetic acid (2.6
8), bromoacetic acid (2.72), iodoacetic acid (2.98), mercaptoacetic acid (3.43), acetic acid having a substituent such as vinylacetic acid (4.12), halopropionic acid such as chloropropionic acid (2.71-3.92), Aminobutyric acid (4.03), acrylic acid (4.26), etc., aliphatic polycarboxylic acid [malonic acid (2.65), succinic acid (4.00), glutaric acid (4.13), adipic acid (4.26), pimelic acid (4.31) , Azelaic acid (4.39), fumaric acid (2.85), etc.], oxycarboxylic acid [glycolic acid (3.63), lactic acid (3.66), malic acid (3.
24), tartaric acid (2.82-2.99), citric acid (2.87), etc., aldehyde acid or ketone acid [glyoxylic acid (3.
18), pyruvic acid (2.26), levulinic acid (4.44), etc.], aromatic monocarboxylic acid [anilinesulfonic acid (3.
74-3.23), benzoic acid (4.20), aminobenzoic acid (2.02-
3.12), chlorobenzoic acid (2.92-3.99), cyanobenzoic acid (3.60-3.55), nitrobenzoic acid (2.17-3.45), hydroxybenzoic acid (4.08-4.58), anisic acid (4.09-4.4)
8), benzoic acid having substituents such as fluorobenzoic acid (3.27-4.14), chlorobenzoic acid, bromobenzoic acid (2.85-4.00), iodobenzoic acid (2.86-4.00), salicylic acid (2.81), naphthoic acid ( 3.70-4.16), cinnamic acid (3.88), mandelic acid (3.19), etc.], aromatic polycarboxylic acids [phthalic acid (2.75), isophthalic acid (3.50), terephthalic acid (3.54), etc.], heterocyclic Monocarboxylic acid [nicotinic acid (2.05), 2-furancarboxylic acid (2.97)
And the like, and heterocyclic polycarboxylic acids [2,6-pyridinedicarboxylic acid (2.09) and the like].

Organic acids include amino acids [ie, amino acids and amino acid derivatives (substituted amino acids,
A peptide composed of about 5 amino acids, etc.)]. Examples of the amino acids include amino acids [asparagine (2.14), aspartic acid (1.93), and adenine (4.
07), alanine (2.30), β-alanine (3.53), arginine (2.05), isoleucine (2.32), glycine (2.
36), glutamine (2.17), glutamic acid (2.18), serine (2.13), tyrosine (2.17), tryptophan (2.
35), threonine (2.21), norleucine (2.30), valine (2.26), phenylalanine (2.26), methionine (2.15), lysine (2.04), leucine (2.35), etc.],
Amino acid derivatives [adenosine (3.50), adenosine triphosphate (4.06), adenosine phosphate (3.65-3.80), L-
Alanyl-L-alanine (3.20), L-alanylglycine (3.10), β-alanylglycine (3.18), L-alanylglycylglycine (3.24), β-alanylglycylglycine (3.19), L-alanine Luglycylglycylglycine (3.18), glycyl-L-alanine (3.07), glycyl-β-alanine (3.91), glycylglycyl-L-
Alanine (3.18), glycylglycylglycine (3.2
0), glycylglycylglycylglycine (3.18), glycylglycyl-L-histidine (2.72), glycylglycylglycyl-L-histidine (2.90), glycyl-
DL-histidylglycine (3.26), glycyl-L-histidine (2.54), glycyl-L-leucine (3.09),
γ-L-glutamyl-L-cysteinylglycine (2.0
3), N-methylglycine (sarcosine, 2.20), N,
N-dimethylglycine (2.08), citrulline (2.43),
3,4-dihydroxyphenylalanine (2.31), L-
Histidylglycine (2.84), L-phenylalanylglycine (3.02), L-prolylglycine (3.07), L-
Leucyl-L-tyrosine (3.15) and the like ".

The acid is usually an organic acid, for example, an aliphatic monocarboxylic acid [formic acid, haloacetic acid such as chloroacetic acid, etc.]
Saturated or unsaturated C such as halopropionic acid and acrylic acid
_1-3 monocarboxylic acids, etc.], aliphatic polycarboxylic acids [saturated or unsaturated C _2-4 dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, fumaric acid, etc.], oxycarboxylic acids [glycolic acid, lactic acid , malic acid, tartaric acid, C _1-6 hydroxycarboxylic acid such as citric acid, is often used an amino acid or a derivative thereof. These acids may be water-insoluble or water-soluble.

The acid may be used as a free acid or as an alkali metal salt or an alkaline earth metal salt. Examples of the alkali metal include lithium, potassium, and sodium, and examples of the alkaline earth metal include calcium, magnesium, barium, and strontium. Preferred alkali metals include sodium, and preferred alkaline earth metals include calcium and magnesium. These alkali metals and alkaline earth metals can be used alone or in combination of two or more, and the alkali metal and the alkaline earth metal may be used in combination.

The total content of the acid and its metal salt is determined by
A range that does not impair releasability, transparency, spinnability, etc., for example,
1 × 10 per 1 g of cellulose acetate^-9~ 3 × 1
0^-FiveMol, preferably 1 × 10^-8~ 2 × 10^-FiveMole (example
For example, 5 × 10^-7~ 1.5 × 10^-FiveMol), even more preferred
Or 1 × 10^-7~ 1 × 10^-FiveMoles (eg 5 × 10
^-6~ 8 × 10^-6Mol) range, usually
5 × 10^-7~ 5 × 10 ^-6Mol (for example, 6 × 10^-7~ 3
× 10^-6Mol).

The content of the acid and the metal salt thereof in the cellulose acetate can be determined by the following method. [Ion Chromatography Analysis] 2.0 g of dried cellulose acetate in the form of fine powder is accurately weighed, and 80 ml of hot water is added thereto. The mixture is stirred, left closed overnight, and further stirred to settle the sample. About 10 ml of the supernatant is used as a sample solution, and the content of the acid is measured by ion chromatography.

[Cellulose Acetate of Embodiments (3), (5), (6) and (7)] In the cellulose acetate of Embodiments (3), (5), (6) and (7), alkali metal and alkaline earth in 1 g of cellulose acetate are used. By reducing the total content of similar metals,
Improves film peelability, transparency and spinnability by casting. Examples of the alkali metal and the alkaline earth metal include the same metals as described above. Cellulose acetate is
One of the alkali metal and the alkaline earth metal may be contained alone, or both the alkali metal and the alkaline earth metal may be contained.

These alkali metals and / or alkalis
When the content of earth metals is low, cellulose acetate
Acid groups (carboxyl groups, sulfonic acid groups, etc.)
May be combined. Al in 1 g of cellulose acetate
The total content of potassium and alkaline earth metals is
Above the effective amount which does not impair heat stability of acetate
And 5.5 × 10 in ion equivalent^-6Below equivalent (example
For example, 0.01 × 10 ^-6~ 5 × 10^-6Equivalent), preferably
Is 3.5 × 10^-6Equivalent or less (for example, 0.01 × 10^-6
~ 3 × 10^-6Equivalent), more preferably 2.5 × 10^-6
Equivalent or less (for example, 0.01 × 10^-6~ 2 × 10^-6This
Volume). In particular, alkali metals and alkaline earths
1 × 10 total metal content^-6Equivalent or less (for example, 0.
1 × 10^-6~ 0.5 × 10^-6Equivalent), especially 0.3 × 10
^-6Equivalent or less (for example, 0.1 × 10 ^-6~ 0.3 × 10^-6
(Equivalent) of cellulose acetate
The dope is cast on the support by the
When peeling from the support, the peel resistance can be greatly reduced.
You. In addition, alkali metal and cellulose in cellulose acetate
And alkaline earth metal content are determined by atomic absorption analysis.
We can measure.

The cellulose acetate of the above embodiments (1) and (2) is, for example, a mixture of cellulose acetate and an acid having an acid dissociation index pKa or a metal salt thereof, or a treatment of cellulose acetate with the acid or a metal salt thereof. Can be prepared. The mixing or treatment of the acid or its metal salt is as follows:
It can be carried out in an optional step, for example, a production step of cellulose acetate (for example, a step of adding a heat stabilizer after completion of the hydrolysis / ripening step, etc.) or after production of cellulose acetate. The treatment with an acid or a metal salt thereof may be performed by washing, dipping, impregnating, or the like of powdery or flaky cellulose acetate. Further, the mixing or treatment may be performed by adding an acid or a metal salt thereof to a dope containing cellulose acetate. The mixing or treatment of the acid having an acid dissociation index pKa or a metal salt thereof is performed at an appropriate temperature that does not impair workability, for example,
The reaction can be performed at a temperature of about 10 to 70 ° C (preferably 15 to 50 ° C), and the mixing or treatment time can be selected from an appropriate range, for example, a range of about 1 minute to 12 hours. When such an acid having a specific pKa or a metal salt thereof is used, at least a part of the carboxyl groups bonded to cellulose acetate and / or hemicellulose acetate can be present as an acid-type carboxyl group.

The cellulose acetate of the above-mentioned embodiment (3) can be prepared, for example, by reducing the amount of a heat-resistant stabilizer (alkali metal salt or alkaline earth metal salt) added to the cellulose acetate in the cellulose acetate production process, Then, the cellulose acetate can be prepared by treating the cellulose acetate with a metal salt of an acid having the acid dissociation index pKa.

In the above-mentioned embodiment (4), that is, cellulose acetate having an acid type carboxyl group (aspect (1)) and containing an acid having a specific pKa or a metal salt thereof (aspect (2)) As described above, a specific acid or a metal salt thereof is contained in cellulose acetate by mixing (addition) or treatment, and at least a part of the carboxyl groups bonded to cellulose acetate and / or hemicellulose acetate is converted into an acid type carboxyl group. Can be prepared.

In the embodiment (5), that is, cellulose acetate having an acid type carboxyl group (aspect (1)) and having a reduced content of alkali metals and alkaline earth metals (aspect (3)), The amount of the heat stabilizer (alkali metal salt or alkaline earth metal salt) added to cellulose acetate can be adjusted or the above pK can be added to cellulose acetate.
It can be prepared by mixing a metal salt of the acid (a) (alkali metal salt, alkaline earth metal salt), or treating cellulose acetate with the metal salt of the acid.

The embodiment (6), that is, a specific pKa
Cellulose acetate containing an acid having the formula (I) or a metal salt thereof (Embodiment (2)) and having a reduced content of alkali metal and alkaline earth metal (Embodiment (3)) has a specific pKa
Can be prepared by adjusting the addition amount of an acid or a metal salt thereof having an alkali metal or an alkaline earth metal together with the addition amount of an acid or a metal salt thereof having a specific pKa.

The embodiment (7), that is, an acid having a carboxyl group of an acid type (embodiment (1)), an acid having a specific pKa or a metal salt thereof (embodiment (2)), and an alkali metal and Reduced alkaline earth metal content (aspect
(3)) As described above, the amount of the acid or the metal salt thereof having a specific pKa is adjusted by mixing (adding) or treating the cellulose acetate. It can be prepared by adjusting the addition amount of the alkali metal and the alkaline earth metal together with the addition amount.

Such a cellulose acetate has a high releasability from a support in the production of a film by a casting method, and can improve the film formation rate and, consequently, the productivity of the cellulose acetate film. Further, cellulose acetate is excellent in optical properties such as transparency. The transparency of cellulose acetate is, for example, 60 to 100% (preferably 70 to 100%, more preferably 75 to 10%).
0%), usually about 70 to 90%, and haze is about 1 to 8 (preferably 1 to 5). Further, the Yellowness Index (YI) as an index of the yellowness of cellulose acetate is, for example, about 1 to 10 (preferably 1 to 7, usually 2 to 5). The transparency, haze, and yellowness index (YI) are values measured by the following method.

[Transparency] 8.0 g of dried cellulose acetate was accurately weighed, and the solvent (methylene chloride / methylene chloride /
125.3 g of a mixed solvent of methanol = 9/1 (weight ratio) or acetone) is added to completely dissolve (6% by weight sample solution). Cesium photoelectric tube, filter No. 12
Using an AKA photoelectric colorimeter equipped with
The transmittance is measured by placing the sample in a 00 mm glass cell, and the measured value is used as a blank. Next, a 6% by weight sample solution was passed through an optical path length of 100 mm.
The transmittance was measured in a glass cell of
The transmittance of the sample solution at 0% is defined as the transparency of the sample.

[Haze] 12.0 g of dried cellulose acetate is accurately weighed, and 88.0 g of a solvent (mixed solvent of methylene chloride / methanol = 9/1 (weight ratio), acetone, etc.) is added and completely dissolved. (12% by weight sample solution). Using a turbidity meter (manufactured by Nippon Denshoku Industries), a glass cell (width 45 mm, height 45 mm, optical path length 10 m)
Using m), measure as follows. The solvent is put in a glass cell, set on a turbidimeter, and zero-point alignment and standard alignment are performed. Next, a 12% by weight sample solution is put into a glass cell, set on a turbidimeter, and the numerical value is read.

[Yellowness Index (YI)] 12.0 g of dried cellulose acetate was accurately weighed, and a solvent (methylene chloride / methanol = 9/1) was used.
88.0 g of a (weight ratio) mixed solvent or acetone is added and completely dissolved (12% by weight sample solution). Using a color difference meter (manufactured by Nippon Denshoku Industries, color difference meter # 90) and a glass cell (width 45 mm, height 45 mm, optical path length 10 mm),
YI is calculated by the following formula. YI = YI ₂ −YI ₁ (wherein, YI ₁ represents the YI value of the solvent, and YI ₂ represents the YI value of the 12% by weight sample solution.) Further, the cellulose acetate of the above embodiment is characterized by a solution stability, filterability, The spinning characteristics are also excellent, and the frequency of yarn breakage can be greatly reduced even when spinning is performed continuously over a long period of time.

Further, by adjusting the pH of the flake slurry to 4.5 to 6.0 by using the acid and the salt thereof of the present invention, the flake slurry has high releasability, optical properties and spinnability, and has high heat stability. Cellulose acetate having high properties can be obtained. The slurry pH can be measured by the following method.

[Slurry pH] Fine powdery dried cellulose acetate (2.0 g) was accurately weighed, and 80 ml of boiling distilled water was added thereto.
The mixture is further stirred to settle the sample. About 10 ml of the supernatant is used as a sample solution, and the pH is measured with a corrected pH meter.
As a blank, the pH of the boiling distilled water was also measured, and the hydrogen ion concentration [H ⁺ ] of the sample solution and the blank solution was calculated according to the calculation formula [H ⁺ ] = 10 ^{− ( pH)} (pH indicates the measured pH value). _s and [H ⁺ ] _b (s indicates a sample, b indicates a blank) are calculated respectively. [H ⁺ ] _s ≧ [H ⁺ ] _b
Where, the slurry pH can be calculated by the following equation: The slurry ^{pH = -log ([H +]} s - [H +] b) In the case of _{^{[H +] s <[H}} +] b, equation [OH ^-] =
The hydroxyl ion concentrations [OH ⁻ ] _s and [OH ⁻ ] _b of the sample solution and the blank solution can be calculated from 10 ⁻¹⁴ ÷ [H ⁺ ], respectively, and the slurry pH can be calculated by the following equation. Slurry pH = 14 + log ([OH ⁻ ] _s − [O
H ⁻ ] _b +10 ⁻⁷ ) When the cellulose triacetate is treated (washed or dipped) with a cellulose acetate (for example, powdery or flaky cellulose acetate), the acid and / or
Alternatively, it can be produced by adjusting the concentration of the salt thereof and adjusting the pH of the aqueous solution. Note that the treatment mentioned here can be performed in any step during the production process of cellulose acetate, or can be performed after the production of cellulose acetate.

The cellulose acetate of the present invention having such properties can be obtained by using a cellulose acetate solution (dope).
Is useful for producing films and fibers.
The dope of the present invention contains at least one kind of cellulose acetate of the above embodiments (1) to (7). Another dope of the present invention comprises: (a) cellulose acetate;
(B) The acid dissociation index pKa in the aqueous solution is 1.93 or more.
And at least one selected from the group consisting of at least one acid of 4.50, an alkali metal salt of the acid, and an alkaline earth metal salt of the acid. In the latter dope, (a) the cellulose acetate may be the cellulose acetate of the above embodiments (1) to (7),
A normal cellulose acetate other than the above embodiments (1) to (7), that is, a carboxyl group bonded to cellulose acetate and / or hemicellulose acetate is not an acid form but a salt form (alkali metal salt, alkaline earth metal salt). Cellulose acetate, the total content of alkali metals and alkaline earth metals per gram, and cellulose acetate in an amount exceeding 5.5 × 10 ⁻⁶ equivalent in terms of ion equivalent can also be used, and the average degree of acetylation of cellulose acetate can be improved.
The degree of polymerization and the like can be selected from the same range as the cellulose acetate of the present invention.

The dope is usually composed of cellulose acetate and a solvent (organic solvent). As the solvent, depending on the average degree of acetylation of cellulose acetate and the like,
For example, halogenated hydrocarbons (methylene chloride,
Ethylene ketones), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), esters (formate esters such as ethyl formate, acetate esters such as methyl acetate, ethyl acetate, ethyl lactate, etc.), ethers (dioxane, It can be selected from dimethoxyethane, etc.), cellosolves (eg, methyl cellosolve, ethyl cellosolve), cellosolve acetates (eg, methyl cellosolve acetate, ethyl cellosolve acetate), and mixtures thereof. The solvent is
Nitro compounds (nitromethane, nitroethane, nitropropane, etc.), lower alcohols (methanol, ethanol, isopropanol, butanol, diacetone alcohol, etc.) may be contained. The amount of the solvent to be used can be selected within a range that does not impair castability, spinnability, handleability, and the like in film forming. For example, 150 to 1,000 parts by weight (concentration of cellulose acetate = about 10 parts by weight) per 100 parts by weight of cellulose acetate -40% by weight)
And preferably about 200 to 900 parts by weight (concentration of cellulose acetate = about 10 to 30% by weight), and the content of cellulose acetate is usually about 10 to 25% by weight (for example, 10 to 20% by weight). It is.

The dope thus obtained is useful for forming a film by a casting method. In film formation, usually, cellulose diacetate to cellulose triacetate (particularly, cellulose triacetate) is used. The film by the casting method is usually obtained by casting a dope on a support, partially drying the dope, peeling the dope from the support, and then drying. As the support, a conventional support, for example, a mirror-finished metal support (for example, a stainless steel support) can be used. As described above, the cellulose acetate of the present invention has a high releasability (release property) from the support, so that the film in a semi-dry state can be smoothly released from the support, and a cellulose acetate film having a high surface smoothness is obtained. be able to. Therefore, the method using the dope of the present invention is useful as a method for improving the peelability of the film from the support. In addition, since the cellulose acetate film of the present invention is composed of the cellulose acetate, the optical characteristics (yellowness,
Haze and transparency). The thickness of the cellulose acetate film thus obtained is, for example, 5 to 500 μm, preferably 10 to 200 μm, depending on the use.
μm, more preferably 20 to 150 μm (particularly 50 to 150 μm).
150 μm). Incidentally, the cellulose acetate of the present invention is not only useful for forming a photographic film, a protective film for a polarizing plate, a film for a color filter, and the like by the casting method,
Since it has excellent releasability from a support, it can be used for producing a thin optical film by a spin coating method or the like.

As described above, the cellulose acetate of the present invention is excellent in dope stability, filterability and spinnability. When producing a fiber by a spinning method, as the cellulose acetate, usually, cellulose diacetate to cellulose triacetate is used. Spinning can be obtained by a conventional method, for example, by spinning a dope from a spinneret having a large number of pores and drying the dope, and may be stretched if necessary. When the dope of the present invention is spun, clogging of the die pores and breakage of the yarn can be prevented over a long period of time.
Therefore, the method using the dope of the present invention is useful as a method for improving spinnability.

The cellulose acetate and dope of the present invention may be used as a plasticizer, for example, triphenyl phosphate (T
PP), phosphate esters such as tricresyl phosphate (TCP), dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DB)
P), phthalic acid esters such as dioctyl phthalate (DOP) and di-2-ethylhexyl phthalate (DEHP), fatty acid esters such as butyl oleate, methylacetyl ricinoleate, dibutyl sebacate, acetyltriethyl citrate (OACTE), citrate Citrates such as acetyl tributyl acrylate (OACTB);
It may contain trimet acid ester and the like. One or more of these plasticizers can be used. Cellulose acetate may contain a deterioration inhibitor, for example, an antioxidant, an ultraviolet absorber, a peroxide decomposer, a radical inhibitor, a metal deactivator, an acid scavenger, and the like. Furthermore, if necessary, the cellulose acetate may contain other additives,
For example, it may contain a crystal nucleating agent, an inorganic powder (for example, diatomaceous earth, calcium carbonate, titanium oxide, and the like), a heat stabilizer, a flame retardant, a coloring agent, and the like.

[0047]

Industrial Applicability The cellulose acetate of the present invention (cellulose acetate having a carboxyl group in an acid form, cellulose acetate containing a specific acid or its metal salt, cellulose acetate having a small content of alkali metal salt and alkaline earth metal salt) In the case of (1), a film having high releasability from the support in the casting method and having high surface smoothness and optical characteristics can be obtained. Further, the cellulose acetate of the present invention has excellent dope stability, filterability, spinnability and heat resistance.

[0048]

EXAMPLES The present invention will be described below in more detail with reference to Examples, but the present invention is not limited to these Examples. In addition, the peelability of the film by the casting method was evaluated as follows. Cellulose acetate 10
0 part by weight is mixed with 320 parts by weight of methylene chloride, 40 parts by weight of methanol, 25 parts by weight of butanol and 15 parts by weight of triphenyl phosphate (TPP) to prepare a dope. Keep this dope at room temperature (20-25 ° C)
And a thickness of 1 on a smooth stainless steel plate (support)
It was cast to about mm and left at room temperature for 3 to 4 minutes, and the releasability from the support was evaluated according to the following criteria. ：: Peeling resistance is small, the film can be peeled smoothly, and the film surface is smooth. ×: Peeling resistance is large, the film cannot be peeled smoothly, or the peeled material from the film adheres to the stainless steel plate.

Comparative Example 1 Hardwood kraft pulp (α-cellulose content 94.5)
%) Sprinkle 50 parts by weight of glacial acetic acid on 100 parts by weight to activate the pretreatment, and then 470 parts by weight of glacial acetic acid and 265 parts by weight of acetic anhydride.
A mixture of parts by weight and 8.3 parts by weight of sulfuric acid was added, and esterification was performed by a conventional method. After that, hydrolysis is performed,
Heat stabilizer (calcium acetate and magnesium acetate)
By adding cellulose triacetate having a degree of acetylation of 61.3% and a viscosity average degree of polymerization of 301 (CTA, calcium content: 98 ppm (4.9 × 10 ⁻⁶ ion equivalent), magnesium content: 16 ppm (1.3 × 10 ^-6
Ion equivalent)). The YI of the obtained CTA was 7.
1, the haze was 2.6, and the transparency was 78%. A dope was prepared using the obtained CTA, and the peelability of the film by the casting method was evaluated. The peelability was "x".

Examples 1 and 2 and Comparative Example 2 50 g of the flakes of CTA obtained in Comparative Example 1 were added to aqueous citric acid solutions having different concentrations, and each was added at room temperature (20 to 2).
After stirring for 1 hour at 5 ° C.), the flakes of CTA were separated by filtration, washed with water, and dried under vacuum to obtain 1 g.
Thus, CTA flakes containing the following citric acid were obtained.

Example 1 Citric acid content 7.7 × 10 ^-7 mol,
YI 7.0, haze 2.2, transparency 85% Example 2: Citric acid content 6.8 × 10 ^-8 mol, YI 7.0, haze 2.4, transparency 81% Comparative Example 2: citric acid content 5.5 × 10 ^-9 mol, YI 7.1 , Haze 2.6, transparency 75% The citric acid-treated CT obtained in the same manner as in Comparative Example 1 described above.
When a dope containing A flakes was prepared and the releasability from the support by the casting method was evaluated, the releasability was “○” in Examples 1 and 2, and “X” in Comparative Example 2.
Met.

Example 3 97 g of the dope prepared in Comparative Example 1 (CTA content: 19.
To 4 g), 11.8 mg of citric acid was added and mixed to prepare a dope containing citric acid. Using this dope, the releasability from the support by the casting method was evaluated in the same manner as in Comparative Example 1, and the releasability was “○”.

Example 4 Using the flakes of CTA obtained in Comparative Example 1, a dope was prepared in the same manner as in Comparative Example 1, and 97 g of this dope (C
TA content 19.4 g) calcium citrate · to 4H ₂
35.3 mg of O was added and mixed to prepare a dope containing citrate. Using this dope, the releasability from the support by the casting method was evaluated in the same manner as in Comparative Example 1, and the releasability was “○”.

Comparative Example 3 Hardwood Kraft Pulp (α-cellulose content 94.5)
%) 100 parts by weight of glacial acetic acid was sprinkled with 50 parts by weight to activate the pretreatment, and then 445 parts by weight of glacial acetic acid and 265 parts by weight of acetic anhydride were used.
A mixture consisting of 8.3 parts by weight of sulfuric acid and 8.3 parts by weight of sulfuric acid was added, and esterification was performed by a conventional method. After hydrolysis, cellulose triacetate (CTA) having a degree of acetylation of 60.8% and a viscosity average degree of polymerization of 313 was obtained without adding heat stabilizers (calcium acetate and magnesium acetate).
The calcium content per 1 g of CTA is 0 ppm,
The magnesium content is 7.3 ppm (0.61 × 10 ⁻⁶⁾
(Ion equivalent), the sodium content was 0 ppm, and the obtained CTA had a YI of 3.5, a haze of 2.7, and a transparency of 78.2%.

Examples 5 to 7 and Comparative Examples 4 and 5 The flakes of Comparative Example 3 were immersed in calcium hydroxide aqueous solution, magnesium hydroxide aqueous solution, and sodium acetate aqueous solution having different concentrations, respectively, and then filtered. By drying, CT containing the following metal components per gram
A flake was obtained. In addition, calcium is shown by Ca, magnesium by Mg, and sodium by Na.
The equivalent amount of ion equivalent per 1 g of A (unit × 10 ⁻⁶ equivalent) is shown.

Example 5: Ca content 10 ppm (0.5), Mg content
5.6 ppm (0.47), Na content 0 ppm Example 6: Ca content 6.5 ppm (0.33), Mg content 22 ppm (1.8),
Na content 0 ppm Example 7: Ca content 2 ppm (0.1), Mg content 4.3 ppm (0.36),
Na content 53 ppm (2.3) Comparative example 4: Ca content 98 ppm (4.9), Mg content 16 ppm (1.3),
Na content 0 ppm Comparative Example 5: Ca content 129 ppm (6.5), Mg content 93 ppm (7.8),
Na content 0 ppm Then, using the immersion-treated CTA, a dope was prepared in the same manner as in Comparative Example 1 and the releasability was examined. The dopes of Examples 5 to 7 were all “「 ”, Each of the dopes of Comparative Example 4 and Comparative Example 5 was “×”.
Slurry pH of Comparative Example 3, Examples 5 to 7 and Comparative Example 5
Was as follows. Comparative Example 3: 4.26 Example 5: 4.51 Example 6: 4.83 Example 7: 5.03 Comparative Example 5: 6.45 Comparative Example 3, Examples 5 to 7, and Comparative Example 5 When the releasability of the cellulose acetate was evaluated, the releasability of Comparative Example 3 and Examples 5 to 7 was “○”, and the releasability of Comparative Example 5 was “X”. When the heat resistance of the cellulose acetate of Comparative Example 3, Examples 5 to 7, and Comparative Example 5 was evaluated based on the following criteria, Comparative Example 3 had a heat resistance of “x”, and the heat resistance of Examples 5 to 7 was In Example 5, the heat resistance was “○”. ：: No deterioration or discoloration occurs during heating and drying at 60 ° C. ×: Deterioration and discoloration occur during heating and drying at 60 ° C.

Example 8 Softwood sulphite pulp (α-cellulose content 9
(4.5%) Spray 50 parts by weight of glacial acetic acid into 100 parts by weight to activate the pretreatment, and then add a mixture consisting of 445 parts by weight of glacial acetic acid, 265 parts by weight of acetic anhydride, and 8.3 parts by weight of sulfuric acid. The esterification was carried out by a conventional method. Thereafter, hydrolysis was carried out, and calcium acetate and magnesium acetate were added to obtain cellulose triacetate (CTA) having an average acetylation degree of 61.3% and a viscosity average polymerization degree of 310. Ca content per 1 g of the obtained CTA was 10 ppm.
(0.5 × 10 ⁻⁶ ion equivalent), Mg content is 5.3 pp
m (0.44 × 10 ⁻⁶ ion equivalent) and YI is 6.
6, haze was 2.0, and transparency was 83%. And when the peeling property was examined in the same manner as in Comparative Example 1, the peeling property was “○”.

Example 9 and Comparative Example 6 The esterification was carried out in the same manner as in Example 8 except that the pulp used in Example 8 was replaced with a softwood sulfite pulp (α-cellulose content: 96.1%). went. Thereafter, hydrolysis is performed, and by adding calcium acetate and magnesium acetate, the average degree of acetylation is 55.2%,
Cellulose diacetate (CDA) containing the following metal components per gram was obtained with a viscosity average degree of polymerization of 299. In the parentheses, the ion equivalent conversion amount (unit × 10 ⁻⁶ equivalent) per 1 g of CDA is shown. Example 9: Ca content 10 ppm (0.44), Mg content 6.2 ppm
(0.52), haze 1.9, transparency 82.5% Comparative Example 6: Ca content 125 ppm (6.3), Mg content 18 ppm
(1.5), Haze 6.3, Transparency 73% A 30% by weight acetone solution was prepared using the CDA obtained in Example 9 and Comparative Example 6, and the spinnability was evaluated based on the following stability of the dope over time. When evaluated, Example 9
In the CDA of Comparative Example 6, the spinnability was “○”, and the CDA of Comparative Example 6 was
Then, the spinnability was "x". ：: Dope does not change with time and clogging does not occur at the time of filtration. ×: Dope becomes cloudy or the like with time, resulting in poor stability.
Clogging occurs during filtration

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29L 7:00

Claims (25)

[Claims] 1. Cellulose acetate wherein at least a part of carboxyl groups bonded to cellulose acetate and / or hemicellulose acetate is present in an acid form. 2. An acid dissociation index pKa in an aqueous solution of 1.9.
Cellulose acetate containing at least one acid selected from the group consisting of 3 to 4.50, an alkali metal salt of the acid, and an alkaline earth metal salt of the acid. 3. A cellulose acetate having a total content of alkali metal and alkaline earth metal in 1 g of cellulose acetate of not less than an effective amount and not more than 5.5 × 10 ⁻⁶ equivalent (in terms of ion equivalent). 4. An acid dissociation index pKa in an aqueous solution of 1.9.
At least one selected from the group consisting of at least one acid selected from the group consisting of at least one acid selected from the group consisting of an alkali metal salt of the acid and an alkaline earth metal salt of the acid, and a carboxyl group bonded to cellulose acetate and / or hemicellulose acetate; Cellulose acetate at least partially present in the acid form. 5. The total content of an alkali metal and an alkaline earth metal in 1 g of cellulose acetate is not less than an effective amount and not more than 5.5 × 10 ⁻⁶ equivalent (in terms of ion equivalent), and the cellulose acetate and / or Or cellulose acetate in which at least a part of carboxyl groups bonded to hemicellulose acetate exists in an acid form. 6. An acid dissociation index pKa in an aqueous solution of 1.9.
At least one selected from the group consisting of at least one acid selected from the group consisting of an alkali metal salt of the acid and an alkaline earth metal salt of the acid, and an alkali metal salt and an alkaline earth metal salt in 1 g of cellulose acetate. Cellulose acetate having a total content of not less than an effective amount and not more than 5.5 × 10 ⁻⁶ equivalent (ion equivalent). 7. An acid dissociation index pKa in an aqueous solution of 1.9.
At least one selected from the group consisting of at least one acid selected from the group consisting of an alkali metal salt of the acid and an alkaline earth metal salt of the acid, and an alkali metal salt and an alkaline earth metal salt in 1 g of cellulose acetate. The total content is equal to or more than the effective amount and equal to or less than 5.5 × 10 ⁻⁶ equivalents (in terms of ion equivalents), and cellulose acetate and / or
Alternatively, cellulose acetate in which at least a part of carboxyl groups integrated in hemicellulose acetate is present in an acid form. 8. The method according to claim 3, wherein the total content of alkali metal and alkaline earth metal in 1 g of cellulose acetate is not less than an effective amount and not more than 2.5 × 10 ⁻⁶ equivalent (in terms of ion equivalent). 8. Cellulose acetate according to any one of 5 to 7. 9. The total content of alkali metals and alkaline earth metals in 1 g of cellulose acetate is not less than an effective amount and not more than 1 × 10 ⁻⁶ equivalent (in terms of ion equivalent). The cellulose acetate according to any one of the above. 10. The cellulose acetate according to claim 2, wherein the acid has a pKa of 2.0 to 4.4. 11. The method according to claim 2, wherein the acid is at least one organic acid selected from aliphatic monocarboxylic acids, aliphatic polycarboxylic acids, oxycarboxylic acids, and amino acids or derivatives thereof. The cellulose acetate according to any one of the above. 12. The acid is at least one organic acid selected from saturated or unsaturated C _1-3 monocarboxylic acids, saturated or unsaturated C _2-4 dicarboxylic acids, C _1-6 oxycarboxylic acids and amino acids. The cellulose acetate according to any one of claims 2, 4, 6 to 10. 13. The method wherein the acid is formic acid, haloacetic acid, halopropionic acid, acrylic acid, malonic acid, succinic acid, glutaric acid,
Fumaric acid, glycolic acid, lactic acid, malic acid, tartaric acid, at least one selected from citric acid,
Cellulose acetate according to any one of 4, 6 to 10. 14. The total content of an acid and a metal salt thereof is 1 × 10 ^{−3 to} 3 × 10 ⁻⁵ per 1 g of cellulose acetate.
The cellulose acetate according to any one of claims 2, 4, 6 to 10, which is a mole. 15. The total content of the acid and its metal salt is from 1 × 10 ⁻⁸ to 2 × 10 ⁻⁵ per 1 g of cellulose acetate.
The cellulose acetate according to any one of claims 2, 4, 6 to 10, which is a mole. 16. The total content of the acid and its metal salt is from 1 × 10 ⁻⁷ to 1 × 10 ⁻⁵ per 1 g of cellulose acetate.
The cellulose acetate according to any one of claims 2, 4, 6 to 10, which is a mole. 17. The cellulose acetate according to claim 1, wherein the pH of the slurry is from 4.5 to 5.5. 18. The cellulose acetate according to claim 1, wherein the pH of the slurry is 4.8 to 6.0. 19. The cellulose acetate according to claim 1, which has an average degree of acetylation of 43.7 to 62.5%. 20. Cellulose acetate using sulfuric acid as an acetylation and / or aging catalyst.
Item 10. The cellulose acetate according to any one of Items 9 to 9. 21. The raw material cellulose is at least one of wood pulp and linter pulp.
20. The cellulose acetate according to any one of the items 20. 22. The raw material cellulose is at least one of hardwood pulp and softwood pulp.
21. The cellulose acetate according to any one of the items 21. 23. A dope comprising at least one cellulose acetate according to any one of claims 1 to 22. 24. (a) Cellulose acetate and (b) at least one acid having an acid dissociation index pKa in an aqueous solution of 1.93 to 4.50, an alkali metal salt of the acid and the acid A dope containing at least one selected from alkaline earth metal salts. 25. A method for improving the peelability or spinnability of a film from a support by using the dope according to claim 23 or 24.